The following TLE is based on Kevin Fetter's and my observations of Aug 9-10 UTC: OTV 3 337 X 364 km 1 39025U 12071A 14222.05124835 .00000000 00000-0 00000-0 0 02 2 39025 43.5156 164.2522 0020000 99.4865 260.8427 15.73524265 09 Arc 20140809.05-0810.07 WRMS resid 0.033 totl 0.025 xtrk Based on this solution, I can confidently state that the s/c spent some time in a significantly lower orbit sometime between early Aug 4 UTC and early Aug 9 UTC. Below are its pre-manoeuvre elements: 1 39025U 12071A 14216.09424805 .00000000 00000-0 00000-0 0 09 2 39025 43.5256 200.3762 0019515 34.3091 325.1355 15.72763563 06 As has been noted previously, observers found the object running more than 18 min. early on Aug 9, five days after it was last seen. When I observed it in its present orbit, on Aug 09 at 02:47 UTC, it was about 1115 s early relative the pre-manoeuvre orbit. The present orbit has nearly the same orbital period as the pre-manoeuvre orbit; therefore, it cannot account for the 1115 s early arrival, and there must have been another orbit change in the 5 day interim that could account for early arrival. There are two possibilities. The first is that it manoeuvred to a lower orbit, which would have allowed it to move ahead of where it would have been in the pre-manoeuvre orbit. Alternatively, it could have gone higher, which would have caused it to fall behind the pre-manoeuvre orbit, and given sufficient time, could have caused it more than lap it in reverse, so that it appeared to be early when we observed it on the 9th. The RAAN of the present orbit enables us to determine whether it went lower or higher. A lower orbit would have caused the RAAN to precess westward faster; a higher orbit was have precessed more slowly. My analysis rules out a higher orbit, because the RAAN would have been about 1.4 deg greater than that of the present orbit, well outside the uncertainty in the orbital elements. Time spent in a variety of lower orbits could account for the 1115 s early arrival, and in agreement with the present RAAN to within about 0.2 deg. The present elements could be off by 0.2 deg, but not by 1.4 deg, so the higher orbit can be confidently dismissed. Below are some combinations of orbital altitude and dwell time in that orbit that could account for the early arrival: Alt n0 Period Dwell Km rev/d s d 286 15.96 5407 0.887 302 15.90 5427 1.203 316 15.85 5445 1.710 330 15.80 5462 2.957 336 15.78 5469 4.174 For comparison, here are the corresponding values of the pre and post-manoeuvre orbit, derived from the above elements 351 15.73 5487 pre-manoeuvre 349 15.74 5484 post-manoeuvre I do not know the purpose of the manoeuvre. I speculate that it could have been intended to adjust the ground track, perhaps to optimize observation of some target on the Earth, or in preparation for landing in the not too distant future. For either purpose, I suspect that the combination of a smaller manoeuvre and longer dwell time would have been preferred, to conserve propellants. If there was some urgency, then lower orbit might have been preferred. Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Sun Aug 10 2014 - 11:18:14 UTC
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